FISHING -- Outdoor Life once headlined Montana's Bighorn River as the Best Trout Stream in America.

Apparently the predators heard the news.

A fly fisherman got the surprise of his life last month when he cast for the river's noble trout and hooked up with a lunker northern pike.

Here's the story by Brett French of the Billings Gazette:

Rogue Fish / Fly fisher lands big pike on renowned trout river

By BRETT FRENCH / french@billingsgazette.com

Famed for its spectacular trout fishing, Montana's Bighorn River recently gave Kansas City, Mo., fly angler Nathan Diesel a big, toothy surprise - a 38-inch, 16-pound northern pike.

"How crazy is that?" said Mike DuFresne, a Billings fly angler who rowed Diesel to the spot of the catch, about a mile below the 3-Mile fishing access site.

The catch is so surprising because northern pike aren't common to that stretch of the river, especially ones that big. For about 30 miles below Yellowtail Dam - the portion of the Bighorn River that Diesel and DuFresne were fishing - the Bighorn River flows cool and clear, making it a productive and popular trout fishery, well-known around the world. Rainbow and brown trout are the main species of fish occupying that stretch of water, not northern pike.

"They're not unheard of, but it's pretty rare," said Mike Ruggles, a Fish, Wildlife and Parks fisheries biologist for the Bighorn.

Slow day

The 36-year-old Diesel said his day of fishing on Jan. 23 had been unproductive. They had launched DuFresne's drift boat below the Afterbay that morning, but DuFresne had caught only two trout before they stopped at what's known as Crow Beach.

Using a 6 weight Winston fly rod, Diesel was tossing a 5-inch long articulated fly that he'd tied up only the night before. Diesel is used to casting such big flies. He said on the White River in Arkansas it's common for anglers to lob 6- to 8-inch long articulated flies into the water to catch big brown trout.

On the Bighorn, Diesel was stripping the big fly back to shore when he saw the shadow of a fish in pursuit of the minnow-looking streamer. With only about 3 feet of fly line dangling from the end of the rod, he stopped stripping and twitched the rod tip a few times to give the fly a little action. That's when the big pike inhaled the fly, turned and swam away, peeling off line until reaching the backing.

"I've caught three browns over 20 pounds in my life," Diesel said, the largest weighing 24 pounds. "So I thought it was a brown trout all along."

Not a trout

Diesel yelled to DuFresne, who was fishing above him, to grab the net and that he had a big fish on - at least a 10-pounder. DuFresne arrived in time to see the big fish roll on the surface, that's when they both realized it was a pike and not a brown trout.

"Your brain, when you're on the Bighorn, is in trout mode," DuFresne said, so seeing a northern pike roll didn't register right away since he was trying to decipher if the fish was a rainbow or a brown trout.

Unable to fit more than the pike's head in the trout net, the two anglers boosted the fish onto the bank and marveled at its size. After the first couple of photos, DuFresne talked Diesel into posing with the fish in front of his drift boat while holding the fly rod so they could convince people that the big northern had indeed been caught on the Bighorn River.

"The picture has gone viral in the Billings area," DuFresne said. "Almost everyone who has seen it said, 'Wow, I can't believe you landed it' because pike are notorious for shearing line off."

Toothy predators

Northern pike have rows of super sharp teeth. Most anglers targeting the fish use heavy leaders, or even steel leaders, to prevent the fish from cutting the line and breaking off.

So the fact that Diesel was able to land the fish on more traditional gear makes the outcome even more incredible.

"It took the fly so deep in its throat that we believe the leader stayed in the corner of its mouth away from the teeth," DuFresne said.

Diesel's rod was rigged with 0X fluorocarbon tippet, which is strong but still only rated as 12-pound test. Tied to the end of the tippet Diesel had his large, articulated fly, which is about two times larger than a more standard size 6 woolly bugger fly more commonly used to hook trout on the river.

"My wife affectionately named the fly the Phantom," Diesel said.

Hero shot

Since landing the fish, Diesel has gained a bit of notoriety among DuFresne's fishing buddies. When they see a photo of the fish, most people say "Holy cow," and the second thing they say is "Did you kill it?" he said.

Keeping such a large, predatory fish in the popular trout river wouldn't earn Diesel many fly-fishing fans, but removing it from the water sure has.

"We had to cull her from the herd," DuFresne said. "It was a female. She was actually in spectacular condition, not a mark or mar on her.

"It surprised me as fat as she was that her belly was completely empty, but jam-packed with close to 3 pounds of eggs alone."

Diesel said he doesn't like to eat fish, but DuFresne has already fried up some of the fillets. The fish is so big that one-quarter of its meat fed four people, he said.

The Wanderer

So where did the fish come from?

Northerns have been planted in Tongue River and Fort Peck reservoirs in Montana, as well as Lake Sakakawea in North Dakota. All of them are connected to the Yellowstone River, to which the Bighorn River is a tributary. Yet the mouth of the Tongue River is 100 miles downstream. It's about 300 miles to the Missouri-Yellowstone confluence and Lake Sakakawea.

It's been documented by FWP that high water in 2011 flushed some of Montana's reservoir fish over dams. The Tongue River joins the Yellowstone River at Miles City, and Fort Peck Reservoir feeds the Missouri River, which joins the Yellowstone near the Montana-North Dakota border. The Missouri River feeds Lake Sakakawea in North Dakota. Could this pike have grown up in one of these lakes before wandering?

Northern pike are also known to infrequently inhabit the lower Bighorn River from Hardin downstream, but there are several diversion dams on the Bighorn and Yellowstone rivers any fish migrating upstream would have to cross.

"Pike are pretty good swimmers," said FWP's Ruggles. "It's been documented that those fish will move a long way looking for good spawning habitat."

Diesel also came a long way to defy the odds.

"It's crazy to think about the hundreds and hundreds of boats, the thousands of fishing lines that have gone through that hole," DuFresne said.

He said other anglers may have hooked the fish and quickly been broken off, without knowing it was a large pike.

Diesel and DuFresne finished their Bighorn fishing trip with only a couple of trout apiece - and one enormous pike, the only one Diesel has ever caught.

"It was a slow day," Diesel said. "But one fish can sure make a day."